Production of linear alkyl benzene

ABSTRACT

This invention relates to a process for producing linear alkyl benzene, the process including the steps of obtaining a hydrocarbon condensate containing olefins, paraffins and oxygenates from a low temperature Fischer-Tropsch reaction; a) fractionating a desired carbon number distribution from the hydrocarbon condensate to form a fractionated hydrocarbon condensate stream; b) extracting oxygenates from the fractionated hydrocarbon condensate stream from step (a) to form a stream containing olefins and paraffins; c) combining the stream containing olefins and paraffins from step (b) with the feed stream from step (g) to form a combined stream; d) alkylating olefins in the combined stream from step (c) with benzene in the presence of a suitable alkylation catalyst in an alkylation reactor, e) recovering linear alkyl benzene from the alkylation reactor; f) recovering unreacted paraffins from the alkylation reactor; g) dehydrogenating the unreacted paraffins in the presence of a suitable dehydrogenation catalyst to form a feed stream containing olefins and paraffins; and h) sending the feed stream containing olefins and paraffins from step (g) to step (c).

BACKGROUND OF THE INVENTION

THIS invention relates to a process for producing linear alkyl benzene.

Alkyl benzene derivatives, such as alkyl benzene sulphonates, are amongothers, used in detergent and surfactant product applications.Environmental legislation requires that these products arebiodegradable. It is well known that, to be bio-degradable, it isimportant for the alkyl chain to be linear, i.e. with very little or nobranching and low, if any, quatemary carbons.

In conventional processes for producing linear alkyl benzenes, ahydrocarbon stream is hydrogenated in order to remove contaminants suchas sulphur, nitrogen and oxygen contaminants that may be present.Hydrogenation also converts olefin species in the stream to paraffins.Following the hydrogenation reaction, the resulting paraffin stream isfractionated into various carbon ranges. A carbon range, for example theC₈ to C₁₆ range, which includes branched paraffins, is passed through amolecular sleve. The branched paraffins are rejected as a raffinatestream, whilst the linear paraffins are passed through a dehydrogenationreactor to form an olefin/paraffin mixture. This mixture is then fed toan alkylation plant and reacted with benzene to form linear alkylbenzene (LAB). The linear alkyl benzene is then sulphonated to formlinear alkyl benzene sulphonates (LAS). A problem with this approach isthe relatively high cost of paraffinic starting material and the highcost associated with the production of linear paraffins from kerosenefeedstocks.

United Kingdom Patent No. 669,313 in the name of California ResearchCorporation discloses the use of a hydrocarbon condensate from the

Fischer-Tropsch process as a feedstock in the production of alkylbenzene. This reference is limited to the use of “high temperature”Fischer-Tropsch processes wherein the Fischer-Tropsch reaction iscarried out temperatures of approximately 300° C. and higher, for theproduction of the hydrocarbon condensate. The high temperatureFischer-Tropsch processes were found to be suitable because thehydrocarbon condensate contains a high concentration of olefins, usuallyin the region of around 70%. The preferred catalysts in theFischer-Tropsch process for the production of the hydrocarbon condensatein this reference are iron-containing catalysts. This reference statesthat Fischer-Tropsch feedstock produced results in poor quality LinearAlkyl Benezene due to odour and wetting problems caused by carbonyl i.e.oxygenate content of the Fischer Tropsch feedstock. The preferred methodfor addressing this problem is by adsorption of carbonyl compounds fromthe Fischer Tropsch feedstock using activated carbon and silica gel in aguard bed. This process is only feasible for feeds with low oxygenateconcentrations. Also, in the example in this reference the olefinrecovery is less than 25%, i.e. the olefin content is not preserved.

U.S. Pat. No. 3,674,885 in the name of Atlantic Richfield Company aimsto show that a paraffinlolefin mixture obtained from a Fischer-Tropschreactor can be alkylated together with chlorinated paraffins byoperating the alkylation at elevated temperatures. Fresh Fischer-Tropschfeed is mixed with chlorinated paraffin and charged to the alkylationreactor, the unreacted paraffin is separated and partially activated bychlorination and then mixed with fresh Fischer-Tropsch based feedstockbefore alkylation. A synthetic mixture of dodecane and dodecene is usedin the example to represent Fischer-Tropsch feedstock. This referencedoes not acknowledge the difficulties faced when attempting to useFischer-Tropsch feedstock for alkylation and is not considered to berelevant to the present invention.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a processfor producing linear alkyl benzene, the process including the steps ofobtaining a hydrocarbon condensate containing olefins, paraffins andoxygenates from a low temperature Fischer-Tropsch reaction;

-   -   a) fractionating a desired carbon number distribution from the        hydrocarbon condensate to form a fractionated hydrocarbon        condensate stream;    -   b) extracting oxygenates from the fractionated hydrocarbon        condensate stream from step (a) to form a stream containing        olefins and paraffins;    -   c) combining the stream containing olefins and paraffins from        step (b) with the feed stream from step (g) to form a combined        stream;    -   d) alkylating olefins in the combined stream from step (c) with        benzene in the presence of a suitable alkylation catalyst in an        alkylation reactor;    -   e) recovering linear alkyl benzene from the alkylation reactor;    -   f) recovering unreacted paraffins from the alkylation reactor;    -   g) dehydrogenating the unreacted paraffins in the presence of a        suitable dehydrogenation catalyst to form a feed stream        containing olefins and paraffins; and    -   h) sending the feed stream containing olefins and paraffins from        step (g) to step (c).

Typically, the low temperature Fischer-Tropsch reaction is carried in aslurry bed reactor at a temperature of 160° C.-280° C., preferably 210°C.-260° C., and in the presence of a cobalt catalyst to provide ahydrocarbon condensate containing 60 to 80% by weight paraffins and 10to 30% by weight, typically less than 25% by weight, olefins. Theolefins so produced having a linearity of greater than 92%, preferablygreater than 95%. The paraffins so produced have a linearity greaterthan 92%.

The oxygenates may be extracted, in step (b), by distillation,dehydration or liquid-liquid extraction, preferably liquid-liquidextraction. A light solvent such as a mixture of methanol and water ispreferably used in the liquid-liquid extraction.

In a preferred embodiment of the invention the oxygenate extractionprocess is a liquid-liquid extraction process that preferably takesplace in an extraction column using a mixture of methanol and water asthe solvent, wherein an extract from the liquid-liquid extraction issent to a solvent recovery column from which a tops product comprisingmethanol, olefins and paraffins is recycled to the extraction column,thereby enhancing the overall recovery of olefins and paraffins. Abottoms product from the solvent recovery column may also be recycled tothe extraction column. The solvent preferably has a water content ofmore than 3% by weight, more preferably a water content of about 5%-15%by weight. A raffinate from the extraction column may be sent to astripper column from which a hydrocarbon feed stream containing morethan 90% by weight olefins and paraffins and typically less than 0.2% byweight, preferably less than 0.02% by weight oxygenates exits as abottoms product. Preferably the recovery of olefins and paraffins in thehydrocarbon feed stream is in excess of 70%, more preferably in excessof 80%, while the olefin/paraffin ratio is at least substantiallypreserved.

Typically, the dehydrogenation reaction at step (g) is carried out at aconversion rate of 10%-15%.

Generally, the fractionated hydrocarbon condensate from step (b) willhave an olefin concentration of from 10% to 30% by weight, the feedstream from step (g) will have an olefin concentration of 10% to 15% byweight, and the combined stream at step (c) will have an olefinconcentration of 12.5% to 22.5% by weight.

The invention also relates to a fractionated hydrocarbon condensateproduct from a low temperature Fischer-Tropsch reaction in the C₁₀ toC₁₃ range containing 10 to 30%, typically less than 25%, by weightolefins with a high degree of linearity of greater than 92%, typicallygreater than 95%, for use in a process for manufacturing linear alkylbenzene.

The invention also relates to a linear alkyl benzene product formed fromthe alkylation of olefins which are the product a low temperatureFischer-Tropsch reaction, wherein the linear alkyl benzene product has adegree of linearity of greater than 90%, preferably greater than 93%.

According to a second aspect of the invention there is provided aprocess for producing three hydrocarbon fractions from a hydrocarboncondensate and a wax fraction product stream from a Fischer-Tropschreaction, the hydrocarbon fractions being:

-   1) hydrocarbon fraction A, being a hydrocarbon fraction having a    boiling point above 25° C. and an end point below 200° C.;-   2) hydrocarbon fraction B including at least a mixture of alkanes,    olefins and oxygenates having a boiling point in the range 100-300°    C.; and-   3) hydrocarbon fraction C having a boiling point in the range    120-400° C.; the method including the steps of:    -   i) fractionating the hydrocarbon condensate stream, or a        derivative thereof, from the Fischer-Tropsch reaction to form at        least three fractionated hydrocarbon condensate streams wherein        at least one of the three fractionated hydrocarbon condensate        streams is hydrocarbon fraction B;    -   b) hydroconverting at least the wax fraction product stream, or        a derivative thereof, from the Fischer-Tropsch reaction;    -   c) fractionating the hydroconverted wax product from step b) to        obtain at least a hydroconverted light hydrocarbon stream and a        hydroconverted distillate stream; and    -   d) selectively blending the products of steps a) and c) to        obtain hydrocarbon fractions A and C; and    -   e) transferring the hydrocarbon condensate stream from step (a)        that constitutes hydrocarbon fraction B to a process for the        production of linear alkyl benzenes.

The process may include the additional step of transferring a waxyunconverted fraction from step b) to a process for the production ofhigh viscosity index base oils by either solvent extraction or catalyticisodewaxing.

Typically, the Fischer-Tropsch reaction is a low temperatureFischer-Tropsch reaction carried out in a slurry bed reactor at atemperature of 160° C.-280° C., preferably 210° C.-260° C., and in thepresence of a cobalt catalyst to provide a hydrocarbon condensatecontaining 60 to 80% by weight paraffins and 10 to 30% by weight,typically less than 25% by weight, olefins.

Typically, the hydrocarbon fraction A has a boiling point above 30° C.and an end point below 175° C., preferably below 160° C.

Typically, the hydrocarbon fraction B has a boiling point in the rangeis 145-255° C., and preferably the temperature range is 165-240° C.

Typically, the hydrocarbon fraction C has a boiling point in the range150-380° C., more typically 160-360° C.

The process for the production of linear alkyl benzenes referred to instep e) may comprise alkylation and catalytic dehydrogenation.

According to another aspect of the invention there is provided a processfor producing an additional hydrocarbon fraction being hydrocarbonfraction D including medium to high molecular mass alkanes, both linearand isomerised, having a boiling point typically above 380° C., moretypically above 400° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a process according to a first aspect ofthe invention for producing linear alkyl benzene;

FIG. 2 is a block diagram of a process for extracting oxygenates from ahydrocarbon product, used in the process of FIG. 1; and

FIG. 3 is a block diagram of an integrated process according to a secondaspect of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

This invention relates to the use of a hydrocarbon condensate streamfrom a low temperature Fischer-Tropsch reaction in the production oflinear alkyl benzene.

In the Fischer-Tropsch process, synthesis gas (carbon monoxide andhydrogen), obtained from gasification of coal or reforming of naturalgas is reacted over a Fischer Tropsch catalyst to produce a mixture ofhydrocarbons ranging from methane to waxes and smaller amounts ofoxygenates.

In a low temperature Fischer-Tropsch reaction, the reaction takes placein a slurry bed reactor or fixed bed reactor, preferably a slurry bedreactor, at a temperature in the range of 160° C.-280° C., preferably210° C.-260° C., and a pressure in the range of 18-50 bar, preferablybetween 20-30 bar, in the presence of a catalyst. The catalyst mayinclude iron, cobalt, nickel or ruthenium. However, a cobalt-basedcatalyst is preferred for the low temperature reaction. Usually, thecobalt catalyst is supported on an alumina support.

During the low temperature Fischer-Tropsch reaction, a lighterhydrocarbon vapour phase is separated from a liquid phase comprisingheavier liquid hydrocarbon products. The heavier liquid hydrocarbonproduct (waxy products) is the major product of the reaction and may,for example, be hydrocracked to produce diesel and naphtha.

The lighter hydrocarbon vapour phase which comprises gaseous hydrocarbonproducts, unreacted synthesis gas and water is condensed to provide a“condensation product” which comprises an aqueous phase and ahydrocarbon condensation product phase.

The hydrocarbon condensation product includes olefins and paraffins inthe C₄ to C₂₆ range, and oxygenates including alcohols, esters,aldehydes, ketones and acids. Typically, the hydrocarbon condensateproduct is fractionated into the C₈ to C₁₆ range, preferably into theC₁₀ to a C₁₃ range.

In the case of a cobalt catalyst, olefins, which are predominantly alphaolefins, only make up approximately 10 to 30%, by weight, of thefractionated hydrocarbon condensation product. Generally, this productwould not be considered useful in an alkylation reaction to form linearalkyl benzene, because of the need to remove oxygenates. Oxygenateremoval is required since oxygenates impair the activity of downstreamcatalysts. This is especially detrimental to solid acid catalysts, suchas UOP's Detal catalyst, since it negatively impacts catalyst lifetime,thereby necessitating more frequent catalyst replacement. However, ithas been found that the olefins have a very high degree of linearity ofgreater than 95% and, even though they only make up 10 to 30%, by weightof the hydrocarbon condensate product, it is an excellent feed for theproduction of linear alkyl benzene and provides an economicallyadvantageous manner for the production of highly linear alkyl benzene.The paraffins in the hydrocarbon condensate product also have a highdegree of linearity. These paraffins do not react in the alkylationreaction and are recovered as a high quality paraffin product which isdehydrogenated and recycled to the alkylation reaction. The reactorproduct from the dehydrogenation process has a relatively low olefinconcentration (10%-15% by weight), and the combination of this feedstream with hydrocarbon condensate from the low temperatureFischer-Tropsch reaction increases the olefin concentration in thecombined feed provided to the alkylation reaction due to the higherolefin concentration in the hydrocarbon condensate from the lowtemperature Fischer-Tropsch reaction. This results in a reduction in therecycle flow rate which leads to savings in both capital expenditure andoperating costs.

Referring to FIG. 1, by way of example of a first aspect of theinvention, a hydrocarbon condensation product 10 from a low temperatureFischer-Tropsch reaction using a cobalt catalyst contains 20% by weightolefins, 74% by weight paraffins, and 6% by weight oxygenates. Thehydrocarbon condensation product 10 is passed through a fractionationcolumn 12 and a C₁₀-C₁₃ cut 14 is separated therefrom. The cut 14contains 22% by weight olefins, 71% by weight paraffins and 7% by weightoxygenates. The cut 14 is then sent to a oxygenate removal unit 16 wherethe oxygenates 18 are removed to provide a hydrocarbon feed stream 24containing 23% by weight olefins and 77% by weight paraffins and lessthan 0.2%, preferably less than 0.015% by weight oxygenates.

As mentioned above, the olefin concentration in the cut 14 is low. It istherefore desirable to use an oxygenate removal step which preserves theolefin concentration. In the prior art, many methods of extractingoxygenates from hydrocarbon streams are suggested. Such removal methodsinclude hydrogenation, azeotropic distillation, extractive distillation,vapour phase dehydration, liquid phase dehydration and liquid-liquidextraction. It has been found that distillation, liquid-liquidextraction and dehydration processes are preferred as they tend topreserve the olefin concentration. Typically the required recovery ofolefins and paraffins in stream 24 is larger than 70% of the olefins andparaffins in stream 14, while at least substantially preserving theolefin/paraffin ratio.

With reference to FIG. 2, a liquid-liquid extraction process of theinvention includes an extraction column 20. The fractionatedcondensation product of a low temperature Fischer-Tropsch reactiondescribed above 14 is fed into the extraction column 20 at, or near, thebottom thereof and a solvent stream 21 comprising a mixture of methanoland water is fed into the extraction column 20 at or near the topthereof. The solvent stream 21 preferably comprises more than 5% byweight, typically 6% by weight, water. The solvent to feed ratio in thesolvent stream is low, typically less than 1.5, usually about 1.25.

Raffinate 22 from the top of the extraction column 20, which includesolefins and paraffins and a small amount of solvent, enters a raffinatestripper column 23 and a hydrocarbon product stream comprising more than90% by weight olefins and paraffins usually up to 99% by weight olefinsand paraffins and less than 0.2% by weight, preferably less than 0.02%by weight oxygenates exits as a bottoms product 24. The bottoms product24, which shows an overall recovery of over 90% of the olefins andparaffins contains more than 20% by weight α-olefins and more than 70%by weight n-paraffins. Thus, the olefin content of the hydrocarbonproduct (which is intended for use in the production of linear alkylbenzene) has been preserved. A solvent comprising mainly methanol (morethan 90% by weight) and low concentrations of water (less than 5% byweight) and olefins/paraffins (less than 5% by weight) exits as a topsproduct 25 and is returned to the solvent feed stream 21. If it isdesired to recover the bottoms product 24 as a vapour stream, this canbe done by taking a bottoms vapour stream from the column 20. The liquidproduct from the column 20 will then be a very small effluent stream.

An extract 26 is drawn from the bottom of the extraction column 20 andis fed to solvent recovery column 27. A tops product 29 from the solventrecovery column 27 comprises over 90% by weight methanol, and olefinsand paraffins. Up to 60% of the olefins and paraffins from the extract26 are recovered to the tops product 29. The tops product is thenrecycled to the solvent stream 21. The oxygenate content of the topsproduct 29 can be as low as 50 ppm, depending on the solvent to feedratio used in the extraction column 20. A bottoms product 28 from thesolvent recovery column 27 comprises mainly water, oxygenates andolefins/paraffins. This bottoms product 28 forms two liquid phases thatcan be decanted in a decanter 30. The organic phase is an oxygenate,olefin and paraffin stream 31, which leaves the process as a product.The aqueous phase is a stream 32, which is recycled to the extractioncolumn 20. This stream 32 can either enter the extraction column at thetop along with the solvent stream 21, or slightly lower down the column20, to prevent the low amount of oxygenates that will be present in thisstream from appearing in the raffinate stream 22.

Normally, a high-boiling solvent is preferred for liquid-liquidextraction because the solvent recovery steps after extraction requiresless energy than will be the case for a low-boiling solvent. However, ithas been found that a mixture of methanol and water, which is alow-boiling solvent, need not suffer from this drawback, because it canbe effective at low solvent to feed ratios (this can be lower than 1 ifthe required oxygenate extraction is not too severe).

A study of the different azeotropes that exist between components in thefeed and water would lead one to expect that it would not be possible todistil water overhead in the solvent recovery column 27 withoutazeotroping oxygenates overhead as well. Surprisingly, this turns outnot to be the case. Methanol, which does not form azeotropes with any ofthe other species present, prevents the water/oxygenate azeotropes fromdistilling over at the same temperature as the paraffins and olefins.This appears to be due to an extractive distillation effect.Additionally, it is possible to distil the paraffins and olefinsoverhead, while recovering the oxygenates as a bottoms product. This hasthe effect of enhancing the overall paraffin and olefin recovery of theprocess, because the overheads 29 of the solvent recovery column 27 isrecirculated to the extraction column 20, which means that the paraffinsand olefins will be forced to leave the process in the product stream24.

It is therefore possible to have a hydrocarbon stream 24 with a highoverall recovery of olefins and paraffins, without the use of a countersolvent in the extraction column. In this mode of operation, all themethanol, and part of the water (10-50%) are also recovered in theoverhead stream 29.

When operating a solvent recovery column in the manner described above,it is to be expected that certain species may become trapped in thecolumn. These species will tend to build up and in the process causeunstable operation of the solvent recovery column. Such species wouldtypically be heavier olefins and paraffins or lighter oxygenates in thepresent case. Operating the solvent recovery column with a small sidedraw may prevent the build up of such species and thereby result in muchimproved operability of the system.

It is also possible to run the extraction column 20 and the solventrecovery column 27 at different methanol/water ratios. This may bedesirable because a high water content in the extraction column 20 willlead to increased solvent to feed ratios (because of reduced solubilityof oxygenates in the solvent), while a certain amount of water isnecessary to achieve the extractive distillation effect in combinationwith methanol to recover all the paraffins and olefins as overheadproducts in the solvent recovery column 27. The different methanol/waterratios in the two columns (20 and 27) can be achieved by diverting someof the water in stream 32 to stream 26 by means of a stream 33.

After passing the C₁₀-C₁₃ hydrocarbon feed stream mentioned abovethrough the abovementioned oxygenate extraction process using a mixtureof methanol (95% by weight) and water (5% by weight) and a solvent tofeed ratio of 1.25, the purified hydrocarbon feed stream 24 contains 22%by weight olefins, 76% by weight paraffins and less than 0.02% by weightoxygenates. Not only does the extraction process extract oxygenates withgood recovery of olefins and paraffins, it also preserves the olefincontent of the hydrocarbon feed. The recovery of olefins and paraffinsis 89.9%, while the ratio of olefins to paraffins is substantiallypreserved. The purified hydrocarbon feed stream containing olefins isparticularly useful in the production of linear alkyl benzene.

The oxygenate removal process may include a final adsorption step tofurther reduce the oxygenate content to less than 0.015%. The furtherreduced oxygenate level will depend on the requirements of the chosenalkylation system and may be as low as 0.0001%.

Referring back to FIG. 1, according to the invention the liquidhydrocarbon product 24 from the oxygenate removal process 16 is suppliedto an alkylation/dehydrogenation circuit indicated generally by thenumeral 40. The alkylation/dehydrogenation circuit 40 includes analkylation reactor 42 and a dehydrogenation process 44. An alkylationreaction in the alkylation reactor 42 may be carried out by using aFriedel-Crafts type condensation catalyst such as AICI₁₃, H₂SO₄, BF₃, HFor a solid acid catalyst. In the present case, the UOP DETAL™ solid acidcatalyst alkylation technology is used. Typically, the alkylationreaction is carried out at a temperature of greater than 100° C. and apressure of about 300 Pa (abs), in the presence of UOP's proprietaryDETAL™ catalyst (see Smith R. (1991) Linear alkylbenzene byheterogeneous catalysis. PEP Review No. 90-2-4, SRI International).

It is also possible to use reactive distillation (also known ascatalytic distillation) to perform the alkylation step, where thecatalyst is contained inside a distillation column, and the separationof the unreacted reagents and products occur as soon as the products areformed. In this manner the reactor and product purificationfunctionality are partly combined into a single unit operation.

After alkylation, the unreacted benzene is recovered and recycled to thealkylation reactor 42. The paraffins are recovered and are sent to thedehydrogenation process 44. In the present case, the UOP Pacol™dehydrogenation technology is used for activation of the paraffins.

Typically, the dehydrogenation reaction is carried out at 400-500° C.and 300 kPa (abs), in the presence of a modified platinum catalyst on analuminium oxide substrate. Conversion of paraffins to olefins is limitedto 10-15% in order to limit further dehydrogenation of mono-olefins todienes and cyclics. UOP's DEFINE™ and PEP™ processes are used to furtherremove unwanted by-products from the pacolate, that are formed duringdehydrogenation. The DEFINE™ process selectively hydrogenates dienes tothe mono-olefins, whilst PEP™ removes cyclic compounds from thepacolate.

With reference to the alkylation/dehydrogenation circuit 40, anolefin-paraffin feed 46 is introduced into the alkylation reactor 42which is also supplied with. benzene 48. The olefins from the olefinparaffin feed 46 react with the benzene 48 in the alkylation reactor 42to provide linear alkyl benzene 50, unreacted paraffins 52 and unreactedbenzene 54. The unreacted benzene 54 is recycled to the alkylationreactor. The unreacted paraffin 52 is recovered and sent to thedehydrogenation process 44 to produce a paraffin olefin mixture 46Awhich is supplied to the paraffin olefin line 46, and hydrogen 54.

The paraffins 52 leaving the alkylation reactor 42 are of a high qualityand comprise substantially 100% paraffin. In this example, thedehydrogenation process 44 operates at a paraffin conversion of 12% andthe paraffin olefin mixture 46A leaving the dehydrogenerator 44 has aolefin concentration of 12% and a paraffin concentration of 88%. Thehydrocarbon product 28 is introduced mid-way along to the paraffinolefin stream 46. In this example, the hydrocarbon product 24 has anolefin concentration of 23% and a paraffin concentration of 77% and, onmixing with the paraffins and olefins from 46A, form an olefin-paraffinfeed stream 46B with an olefin concentration of 13.5% and a paraffinconcentration of 86.5%. This increase in olefin concentration in theolefin-paraffin feed stream 46 results in a reduction in the recycleflow rate through the dehydrogenation process 44 and alkylation reactor42, for a fixed production of linear alkyl benzene. Thus, an increasedolefin concentration in the olefin-paraffin feed 46 translates intopotential savings in both capital expenditure and operation expenditure.From a capital expenditure perspective, the reduced recycle flow rateallows for a reduction in the size of the dehydrogenation reactor in thedehydrogenation process 44 as well as a reduction in size of thealkylation reactor 42, for a fixed residence time and the reducedparaffin flow rate will allow for a reduction in the size of theparaffin recovery column and ancillary equipment. The operationexpenditure savings include a reduced mass flow rate through thedehydrogenation reactor 44 and results in a reduction in the requiredhydrogen flow rate required for selective hydrogenation of dienes andreduction in the paraffin flow rate will allow for savings in utilitiessuch cooling water, steam (or hot oil) and electricity.

When the alkylation circuit of the process of the present invention istherefore compared with an alkylation circuit of a conventional processfor the production of linear alkylbenzene as described in the backgroundto the invention, it can be concluded that a smaller alkylation circuitis required on a per mass of linear alkyl benzene produced, than for theconventional process.

In a final step of the process, the highly linear alkyl benzene 44 withlinearity greater than 92% is introduced to a sulphonation reactor 52and sulphonated using sulphuric acid, oleum or sulphur trioxide. Sulphurtrioxide is currently the preferred process. The sulphonation processresults in the formation of a highly linear alkylbenzene sulphonates.

The process of the invention makes use of a feed stream in the form of acondensate product from a low temperature Fischer-Tropsch reaction whichwould not be expected feasible for producing linear alkyl benzene. Theprocess produces a desirable highly linear alkyl benzene product, whileat the same time produces a high quality paraffin product which isdehydrogenated and recycled to the alkylation reaction. The feed streamfrom the dehydrogenation process has a relatively low olefinconcentration (10%-15% by weight), and the combination of this feedstream with hydrocarbon condensate from the low temperatureFischer-Tropsch reaction increases the olefin concentration in thecombined feed provided to the alkylation reactor which results insavings in both capital expenditure and operation expenditure.

A second aspect of this invention relates to a process of producing orworking-up three pre-determined hydrocarbon fractions from the productstreams from a Fischer-Tropsch reaction. These three hydrocarbonfractions include:

-   1) a hydrocarbon fraction A having a boiling point above the 25° C.    and more typically above 30° C., and an end point below 200° C.,    preferentially below 175° C. and even more preferentially below 160°    C.,-   2) a hydrocarbon fraction B including a mixture of 60% to 80% by    weight alkanes, 15-30% by weight olefins and 5% to 10% by weight    oxygenates boiling preferentially in the 100-300° C., and more    preferentially in the range 165-240° C. and where the overall    linearity of the mixture is greater than 92%, preferentially greater    than 95%, and-   3) a hydrocarbon fraction C being a hydrocarbon fraction boiling in    the range 120-400° C., more typically in the 150-380° C. and    preferably in the range 240-360° C.

The invention also extends to producing or working-up a fourthhydrocarbon fraction D including medium to high molecular mass alkanes,both linear and isomerised, boiling typically above 380° C. andpreferably above 400° C.

The process as proposed includes the following advantageous features:

-   1) production of an improved synthetic feedstock for producing    linear alkyl benzenes, namely hydrocarbon fraction B; Although    fraction B contains oxygenates and has a low olefin content, it can    surprisingly be utilized economically/advantageously to produce    linear alkyl benzene using the process described in the first aspect    of this invention,-   2) an improvement in the density and heat content of hydrocarbon    fraction C is observed over a process where hydrocarbon fraction B    was not removed;-   3) production of a high viscosity index (HVI) base oil    feedstock—hydrocarbon fraction D. This product can also lead to the    recovery of a hydrogenated wax comprising both normal and isomerised    alkanes; and-   4) production of a high performance feedstock suitable for the    production of lower olefins, as described in technical literature    (Performance of the Sasol SPD Naphtha as Steam Cracking Feedstock,    American Chemical Society—Paper 561940, presented at National    Meeting, Boston, August 2002).

The production or work up method which forms the subject matter of thisaspect of the invention is based on the processing of the two productstreams derived from a Fischer-Tropsch reaction, namely a wax fractionproduct stream and a hydrocarbon condensate:

-   The wax fraction product stream typically has a true boiling point    (TBP) in the range of about 70° C. to 700° C., more typically in the    range 80° C. to 650° C.-   The hydrocarbon condensate typically has a true boiling point (TBP)    in the range −70° C. to 350° C., more typically −10° C. to 340° C.,    usually −70° C. to 350° C.

A typical composition of the wax fraction product stream and thehydrocarbon condensate is set out in Table 1. TABLE 1 (vol % distilled)Hydrocarbon Wax Fraction Distillation Range Condensate Product StreamC5-160° C. 44 3 160-270° C. 43 4 270-370° C. 13 25 370-500° C. NR40 >500° C. NR 28 Total 100 100

The hydrocarbon condensate includes olefins and paraffins in the C₄ toC₂₆ range, and oxygenates including alcohols, esters, aldehydes,ketones, acetals and acids.

An embodiment of this second aspect of the invention is exemplified withreference to FIG. 3. In this embodiment two liquid hydrocarbon productsare separated from the conversion of synthesis gas (syngas) by theFischer-Tropsch reaction in a Fischer-Tropsch reaction unit 8.

The hydrocarbon condensate is collected as stream 10 and transferred toan atmospheric distillation unit (ADU) 12 where it is separated intothree streams. The lighter stream 13 is transferred to a hydrotreater 60for complete saturation and removal of heteroatoms. (This step isoptional to the process.) The resulting product is collected as stream17. A middle stream 14 is collected as a second product and transferredto a linear alkyl benzene processing operation. A heavier hydrocarbonfraction is collected as stream 15 and transferred to a hydroconversionunit 70. The wax fraction product stream 9 from the Fischer-Tropschreaction unit 8, is blended with stream 15 from the ADU 12 before beingsent as stream 7 to the hydroconversion unit 70. Here at least threeproducts are produced as well as a mixture of light hydrocarbons (notshown in the figure) as a gaseous stream. A light hydrocarbon productstream 71 and a heavier hydrocarbon product stream 72 is sent tostorage. There is a fourth stream that is produced—also not shown in thefigure—that includes all heavy unconverted hydrocarbon species. This isusually recycled to extinction within the hydroconversion unit 70. As analternative to the process, a heavy hydroconverted stream can berecovered as stream 73 and made available for the preparation of highvisibility index (HVI) base oils by either solvent extraction orcatalytic dewaxing. These two processing options are well known in theart and are not described in detail here. Should solvent extraction beused, it is possible to obtain as a by-product a highly paraffinichydrogenated wax.

Stream 14, the middle stream from the ADU 12, which contains syntheticolefinic feedstock is sent to linear alkyl benzene processing startingwith unit 16. Unit 160 is an oxygenates removal unit operation asillustrated in FIG. 2. Two streams are obtained from the oxygenateremoval unit 16: an oxygenates rich stream 18 sent to storage, and astream 24 comprising mostly paraffins and olefins. This stream is thestream “B” having a boiling point in the range 100-300° C. The stream 24is sent to the alkylation unit 42 where it is alkylated with benzene 48transferred from storage. The products from the alkylation unit 42 areseparated into two streams: the linear alkyl benzene product 50 and anunconverted stream 52. The latter stream 52, comprising paraffins, issent to the dehydrogenation unit 44 to undergo catalyticdehydrogenation. Once processed, this is returned via stream 46 to thealkylation unit 42.

The two light liquid hydrocarbon streams, hydrotreated product 17 andhydroconverted product 71 are blended to form a highly paraffinic singlestream 19.

Process conditions for hydrotreating and hydroconversion of streams froma Fischer-Tropsch reaction unit can be varied to achieve a wide range ofproduct compositions. The process conditions are usually laboriouslychosen after extensive experimentation to optimise yields, processperformance and catalyst life. Table 2 gives a list of one such set oftypical conditions. TABLE 2 Process Conditions for Hydroprocessing ofthe Fischer-Tropsch Streams Set of Hydrotreating Range HydroconversionRange Conditions Broad Preferred Broad Preferred Temperature, 150-450 250-350 150-450 340-400 ° C. Pressure, bar-g 10-200 30-80  10-200 30-80H₂ rate, 100-2000  800-1600  100-2000  800-1600 m³n/m³ feed ConversionNA NA 30-80 50-70 (note 1)Note 1Expressed as material boiling above 370° C. that disappears during theprocess (mass %)

The extraction step of the invention will now be described in moredetail with reference to the following non-limiting example.

EXAMPLE

This example shows a process according to the invention. The extractioncolumn 20 was run at a solvent to feed ratio of 1.25 and a temperatureof 50° C. The overall olefin/paraffin recovery in the stream 24 was89.9%. The olefin/paraffin ratio in the feed was 1:3.7 and 1.36 postoxygenate extraction. The olefin/paraffin ratio was thereforesubstantially preserved. Extraction column 20 Stream 14 21 22 26 CompFlow Comp Flow Comp Flow Comp Flow (wt %) (kg/hr) (wt %) (kg/hr) (wt %)(kg/hr) (wt %) (kg/hr) Total 100 3000 100 3750 100 2530 100 4220 TotalC10-C13 P/O 92.7 2779.7 2.16 81.0 99.1 2507.9 6.20 261.7 TotalOxygenates 7.3 217.7 0.000 0.000 0.0144 0.365 5.78 243.7 Lights andHeavies 0.057 1.7 0.004 0.144 0.0104 0.263 0.00480 0.202 Water 0.0310.934 6.01 225.6 0.0073 0.184 5.74 242.4 Methanol 0.000 0.000 91.73443.3 0.842 21.31 82.3 3472.0

Raffinate Stripper column 23 Stream 22 25 24 Comp Flow Comp Flow CompFlow (wt %) (kg/hr) (wt %) (kg/hr) (wt %) (kg/hr) Total 100 2530 100 30100 2500 Total C10-C13 P/O 99.1 2507.9 2.63 0.793 99.97 2499.4 TotalOxygenates 0.0144 0.365 0.00163 0.000491 0.0145 0.363 Lights and Heavies0.0104 0.263 0.0887 0.0267 0.00808 0.202 Water 0.0073 0.184 1.52 0.4560.00115 0.0288 Methanol 0.842 21.31 95.4 28.7 0.000 0.000

Solvent Recovery column 27 Stream 26 29 28 Comp Flow Comp Flow Comp Flow(wt %) (kg/hr) (wt %) (kg/hr) (wt %) (kg/hr) Total 100 4220 100 3584 100636 Total C10-C13 P/O 6.20 261.7 2.37 85.1 27.6 175.8 Total Oxygenates5.78 243.7 0.00140 0.0503 42.0 267.0 Lights and Heavies 0.00480 0.2020.00747 0.268 0.00279 0.0177 Water 5.74 242.4 1.30 46.8 29.3 186.6Methanol 82.3 3472.0 96.2 3451.9 1.04 6.63

1-45. (canceled)
 46. A process for producing linear alkyl benzene, theprocess including the steps of obtaining a hydrocarbon condensatecontaining olefins, paraffins and oxygenates from a low temperatureFischer-Tropsch reaction; a) fractionating a desired carbon numberdistribution from the hydrocarbon condensate to form a fractionatedhydrocarbon condensate stream which is the product of a Fischer-Tropschreaction; b) extracting oxygenates from the fractionated hydrocarboncondensate stream from step (a) to form a stream containing olefins andparaffins which is the product of a Fischer-Tropsch reaction; c)combining the stream containing olefins and paraffins from step (b),which is the product of a Fischer-Tropsch reaction, with the feed streamfrom step (g) to form a combined stream; d) alkylating olefins in thecombined stream from step (c) with benzene in the presence of a suitablealkylation catalyst in an alkylation reactor; e) recovering linear alkylbenzene from the alkylation reactor; f) recovering unreacted paraffinsfrom the alkylation reactor; g) dehydrogenating the unreacted paraffinsin the presence of a suitable dehydrogenation catalyst to form a feedstream containing olefins and paraffins; and h) sending the feed streamcontaining olefins and paraffins from step (g) to step (c).
 47. Aprocess according to claim 46, Wherein, in the extraction step b), theratio of olefins to paraffins is substantially preserved.
 48. A processaccording to claim 46, wherein the low temperature Fischer-Tropschreaction is carried in a slurry bed reactor at a temperature of 160°C.-280° C. and in the presence of a cobalt catalyst to provide ahydrocarbon condensate containing 60 to 80% by weight paraffins and 10to 30% by weight olefins.
 49. The process according to claim 48, whereinthe Fischer-Tropsch reaction is carried out at a temperature of 210°C.-260° C.
 50. The process according to claim 46, wherein theFischer-Tropsch reaction is carried out in the presence of a cobaltcatalyst.
 51. The process according to claim 48, wherein the hydrocarboncondensate contains less than 25% by weight olefins.
 52. The processaccording to claim 48, wherein the olefins in the hydrocarbon condensatehave a linearity of greater than 92%.
 53. The process according to claim52, wherein the olefins in the hydrocarbon condensate have a linearityof greater than 95%.
 54. The process according to claim 48, wherein theparaffins in the hydrocarbon condensate have a linearity greater than92%.
 55. The process according to claim 46, wherein the hydrocarboncondensate is fractionated, in step a), into the C₈ to C₁₆ range. 56.The process according to claim 55, wherein the hydrocarbon condensateproduct is fractionated, in step a), into the C₁₀ to C₁₃ range.
 57. Theprocess according to claim 56, wherein the fractionated hydrocarbonproduct contains 10 to 30% by weight olefins with a degree of linearitygreater than 92%.
 58. The process according to claim 46, wherein theoxygenates are extracted, in step (b), by distillation, dehydration orliquid-liquid extraction.
 59. The process according to claim 58, whereinthe oxygenates are extracted by liquid-liquid extraction.
 60. Theprocess according to claim 59, wherein a light solvent is used in theliquid-liquid extraction.
 61. The process according to claim 60, whereinthe light solvent is a mixture of methanol and water.
 62. The processaccording to claim 61, wherein the oxygenate extraction process is aliquid-liquid extraction process that takes place in an extractioncolumn using a mixture of methanol and water as the solvent, wherein anextract from the liquid-liquid extraction is sent to a solvent recoverycolumn from which a tops product comprising methanol, olefins andparaffins is recycled to the extraction column, thereby enhancing theoverall recovery of olefins and paraffins.
 63. The process according toclaim 62, wherein a bottoms product from the solvent recovery column isrecycled to the extraction column.
 64. The process according to claim61, wherein the solvent has a water content of more than 3% by weight.65. The process according to claim 64, wherein the solvent has a watercontent of from 5%-15% by weight.
 66. The process according to claim 62,wherein a raffinate from the extraction column is sent to a strippercolumn from which a hydrocarbon feed stream containing more than 90% byweight olefins and paraffins and less than 0.2% by weight oxygenatesexits as a bottoms product.
 67. The process according to claim 66,wherein the hydrocarbon feed stream contains less than 0.02% by weightoxygenates.
 68. The process according to claim 46, wherein the recoveryof olefins and paraffins in the hydrocarbon feed stream over theextraction step b) is in excess of 70%.
 69. The process according toclaim 68, wherein the recovery of olefins and paraffins in thehydrocarbon feed stream is in excess of 80%.
 70. The process accordingto claim 46, wherein the olefin/paraffin ratio of the fractionatedhydrocarbon condensate stream a) is substantially preserved over theextraction step b).
 71. The process according to claim 46, wherein thedehydrogenation reaction at step (g) is carried out at a conversion rateof 10%-15%.
 72. The process according claim 71, wherein the fractionatedhydrocarbon condensate from step (b) has an olefin concentration of from10% to 30% by weight, the feed stream from step (g) has an olefinconcentration of 10% to 15% by weight, and the combined stream at step(c) has an olefin concentration of 12.5% to 22.5% by weight.